In current spray nozzles for automobiles at least a portion of the orifice protrudes and is permanently located outside of the vehicle proper where the nozzle is directly exposed to bad weather. Under those conditions the nozzle, or at least the protrusion, may freeze up.
A heating device is thus necessary to rapidly de-ice the spray nozzle and to enable it to operate again with the washing liquid circulating freely. In the automotive industry, two methods are known to accomplish this.
In a first method, the liquid inside the supply duct to the orifice is heated to a temperature vastly above 0.degree. C., for instance between 50 and 60.degree. C. Here the heating system consists of a disk-shaped heating device, comprising a variable positive temperature resistor. This type of heating system is made of metal and a ceramic-based compound material. However, there are a number of shortcomings with this method. Since the heating device is located inside the supply duct the connections are complex, costly and not particularly amenable to welding. Further, the dimensions and the shape of the heating device are not efficient from a thermotechnical viewpoint, the more so because when it must be cooled down since high voltages are required.
In a second method, the portion surrounding the protruding orifice of the spray nozzle is heated to a temperature above 0.degree. C. Here the heating device consists of a resistor, whose rating varies according to temperature, and a resistor, whose rating is fixed. The resistors are connected in series. This method also has a number of shortcomings. First, a large surface resistor is necessary to provide efficient heating because of the high thermal load, and because of the series connection, high voltage is required.
The above heating devices are relatively costly, complex to manufacture, and also difficult to miniaturize, such that they cannot be located sufficiently close to the protruding orifice for optimum performance.